An electrostatic chuck including a heater mechanism is commonly employed to support a work piece (e.g., a silicon wafer) in a stationary position during various procedures. For example, electrostatic chucks including heater mechanisms may be used in filming processes such as Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), dry etching, or other processing techniques. Conventional work pieces can have a variety of shapes and sizes. Larger sized work pieces require precise and accurate positioning to perform a successful patterning operation.
A typical example of the conventional electrostatic chuck including a conventional heater mechanism is disclosed in Japanese patent publication No. 7-307377. The publication discloses an insulating substrate with an upper electrostatic chucking layer and a lower heater layer, which is surrounded by an electronically insulating layer of pyrolytic boron nitride (pBN) or other insulating materials.
The prior art electrostatic chuck may be incorporated as part of a conventional work piece supporting device, an example of which is schematically illustrated in FIG. 4. The conventional work piece supporting device includes an electrostatic chuck 10 wherein a source of voltage can be applied to electrostatic ally attract or clamp a work piece 12 to the chucking surface of the electrostatic chuck 10. A control circuit is also used to supply electricity to the lower heater layer of the chuck 10 to heat the mounting surface 11 of the electrostatic chuck 10. Heat transfer then occurs between the mounting surface 11 and the work piece 12 clamped thereto such that the work piece reaches an optimal temperature range suitable for processing the work piece. In order to prevent warping of the chuck 10, the chuck is secured to a metal base 14 by a plurality of bolts 16 or other fastening means.
In order to process a wafer by Metal Organic Chemical Vapor Deposition (MOCVD) or ion doping, the wafer may be subjected to an elevated temperature in the order of 800° C. or higher. Therefore, the work piece 12 must be heated within a relatively high temperature range while being electrostatic ally mounted to the metal base 14. However, in the configuration of the conventional mounting arrangement, a considerable part of the heat to the heater layer would be transferred to the metal base 14, causing the metal base 14 to act as an undesirable heat sink that interferes with proper heating of the wafer 12 to a high temperature range, say 800° C. Indeed, as shown in FIG. 4, the conventional chuck 10 includes a substantially flat plate with a substantially flat lower surface 18 in direct abutting contact with a substantially flat upper surface 20 of the metal base 14. Conduction of heat from conventional chuck 10 to the metal base 14 is enhanced since the substantially flat lower surface 18 is in direct abutting contact with the substantially flat upper surface 20 along substantially the entire width “W” of the chuck 10.
Due to the enhanced heat conductivity between the abutting substantially planar surfaces (18,20), a considerable portion of the heat generated by the heater layer would be transferred to the metal base 14 rather than the work piece 12. Losing heat to the metal base 14 can inhibit heat transfer to the work piece 12 and therefore render it difficult to heat the work piece within a sufficiently high temperature range, for example, above 800° C. Moreover, even if the work piece 12 can be successively heated to such a high temperature range, the clamping force must be decreased due to difference of thermal expansion between the bolts 16 and the chuck 10, resulting in potential failure of the capability of the metal base 14 from inhibiting, such as preventing, warp of the chuck 10. In addition, when the chuck 10 of a flat plate type is heated to an extremely high temperature such as 800° C. or higher, this is transferred to metallic terminals through which electricity is supplied to chucking electrodes of the chuck 10 so that the terminals may also be heated to substantially the same temperature. This may cause inferior electrical contact between the terminals and the chuck body due to difference of thermal expansion there between.
Further, when the electrostatic chuck 10 comprises a substantially flat plate that is mechanically secured to the warp correction metal base 14, as shown in FIG. 4, the effective work piece clamping area of the chucking surface can be decreased by the bolts 16 and or countersunk apertures to accommodate the bolts 16. Moreover, temperature distribution in the surface of the work piece 12 in contact with the chucking surface of the chuck 10 can be uneven due to thermal transfer from the periphery of the chuck 10 to the surrounding environment.
So-called facedown systems wherein the electrostatic chuck is placed with its chucking surface down have recently attracted considerable attention, because these systems tend to prevent or minimize adherence of particles generated during processing of the work piece. Facedown systems would also be advantageous in view of efficiency of reaction gas introduced during work piece processing. However, the device of FIG. 4 including a flat plate that is mechanically secured to a warp-connection base 14 is not applicable to the facedown system in a high temperature condition of 600° C. or higher.